Non-consumable electrode configuration having increased arc starting capabilities

ABSTRACT

There is disclosed a non-consumable electrode for electric arc welding in a highly controlled inert atmosphere. In order to improve the initiating characteristics the rod-shaped electrode has at least one longitudinal edge starting from the end of the rod facing the arc, the edge angle of at least one of said edges being acute.

United States Patent 1191 Hammarlind NON-CONSUMABLE ELECTRODECONFIGURATION HAVING INCREASED ARC STARTING CAPABILITIES [75] Inventor:Alf Martin Hammarlind, Vasteras,

, Sweden 73] Assignee: Aktiebolaget Atomenergi,

Stockholm, Sweden [22] Filed: June 15, 1970 [21] Appl. No.: 46,045

[52] 11.8. C1. ..219/145, 219/74, 219/75, 1 219/130 [51] Int. Cl. ..B23k35/00 [58] 1 Field of Search .1..2l9/1l9, 145, 137, 136, 75, 219/74, 69E [56] References Cited UNITED STATES PATENTS 2,751,482 6/1956 Stepath..219/70 1 51 Feb. 6, 1973 2,025,206 12/1935 Hols'lag ..219/145X FOREIGNPATENTS OR APPLICATIONS France ..219/136 France ..219/136 PrimaryExaminer-R. F. Staubly Assistant Examiner-George A. MontanyeAttorney-Pierce, Scheffler & Parker [57] ABSTRACT the arc, the edgeangle of at least one of said edges being acute.

4 Claims, 7 Drawing Figures POWER sup/=1. Y

A CHAMBER PAIENTEUFEB a ma 3.715561 WORKP/E C E NON CO/VSUMABL ESHIELD/N6 ELECTRODE GAS CHAMBER F g.4

NON-CONSUMABLE ELECTRODE CONFIGURATION IIAvING INCREASED ARC STARTINGCAPABILITIES having a highly controlled atmosphere. Although not limitedthereto, the invention will hereinafter be particularly described inconnection with TIG-welding.

In TIG-welding, (TIG= Tungsten Inert Gas) i.'e. arc welding in an insertatmosphere by means of a non-consumable electrode, usually of wolfram,it is important that the are can be initiated positively andinstantaneously. To facilitate the striking or initiation of the arewithout having the electrode to touch the workpiece, a high-frequencyand high-voltage initiating current is superimposed on the weldingcurrent. In normal TIG- manual welding the initiation is no problem asthe technique of manual welding includes approaching the electrode tothe workpiece at the moment of initiation, until the arc strikes.However, in machine TlG-welding, where the distance between theelectrode and the workpiece is fixed, initiating problems exist. In TIG-welding of reactive metals, such as zirconium and titanium and theiralloys, in a welding chamber, in

which the electrode is completely surrounded by a 'highlypurified inertgas, the initiating problems are remarkable even when theabove-mentioned technique of manual welding is used.

The initiating problems manifest themselves in uncertain ornon-instantaneous initiations, in initiations in an unforeseendirection, i.e. not in the direction of the axis of the electrode, or inno initiation at all. Also, there might appear a voluminous glowingcloud, a corona effect," which heats unintended parts of the workpieceand/or pass over onto the electrode holder to which the electrode isattached, from which solid particles or sorbed gases are set free, saidparticles or gases contaminating the workpiece.

, In TIG-welding in a welding chamber the following :attempts have beenpreviously made in order to solve said initiating problems:

' i a. The initiating voltage has been increased. This step gives aninconsiderable improvement. v b. The electrode has been provided with aclose fitting quartz tube, the length of which being adjusted to haveonly about 2 mm of the end of the electrode exposed. The purpose of thequartz tube was to prevent said corona effect from moving upwards on theelectrode and from wander over onto other parts of the electrode holder.This gives a clear improvement, especially in combination with apointing of the electrode. However, this step gives no complete solutionsince the initiating problems will, nevertheless, appear again ratherfrequently; i the pointed end of the electrode will be rapidly blunted,this giving a deterioration of the initiation; thequartz tube willcontribute in contaminating the weld due to its low boiling point inrelation to the temperature of the arc. w c. A high voltage cold cathodedischarge device (for instance a Penning vacuum measuring tube) has beenused in order to facilitate the initiation by an ionization of the inertgas. Sometimes, the outcome of using this device has been satisfactory,sometimes it has been a complete failure and, consequently, said deviceis not reliable.

Thus, no one of said steps gives a satisfactory result. Accordingly, itis main object of this invention to provide a novel and improvedelectrode by which said initiating problems are overcome. According tothe invention the electrode has the shape of a rod, the part of whichfacing the arc has at least one longitudinal edge formed between twocontiguous longitudinally extending surfaces starting from the end ofthe rod, the electrode being characterized in that the edge angle of atleast one of said edges is acute, i.e., preferably about 60.

A preferred embodiment of the electrode according to the invention ischaracterized in that each cross section of said part has the shape ofan equilateral triangle.

A further embodiment of the electrode according to the invention ischaracterized in that each cross section of said part has the shape of aregular figure having four angles, said angles being connected byconcave lines.

Said part of the rod facing the arc can be tapered towards the end ofthe rod. Possibly, said part can be pointed.

The electrode according to the invention will be more fully described inthe following specification in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a side view of a preferred embodiment of the electrodeaccording to the invention.

FIG. 2 is a bottom plan view of the electrode illustrated in FIG. 1.

FIG. 3 is a side view of an electrode according to FIG. 1 which has beentapered towards the end of the electrode.

FIG. 4 is a bottom plan view of the electrode illustrated in FIG. 3.

FIG. 5 is a cross sectional view of the electrode illustrated in FIG. 1taken along the line VV.

FIGS. 6 and 7 are cross sectional views illustrating other embodimentsof the electrode according to the invention.

Referring to FIGS. 1 and 2, the end part. of a preferred electrodeaccording to the invention isillustrated. The rod-shaped electrode has acylindrical body 1, the part 3 of which facing the workpiece has beenground, each cross section of said part having the shape of aequilateral triangle (cf. FIG. 5). Thus, said part 3 shows threelongitudinal edges 4 starting from theend 2 of the electrode. The edgeangles a of the edgesare 60. The end 2 of the electrode has been groundflat.

The electrode according to FIGS. 3 and 4 has a part I 6 tapering towardsthe end 7, said part three longitudinal edges 8. v A

FIG. 5 shows a cross sectional view of the electrode according to FIG. 1taken along the IineV-V and illustrating the edge angle a. I

also showing Referring now to H68. 6 and 7, other possible crosssections of electrodes according to the invention are illustrated. Anelectrode having a cross section according to FIG. 6 shows four concavesides, while an electrode having a cross section according to FIG. 7shows two convex sides. Thus, the electrodes have four and twolongitudinal edges, respectively.

Comparative tests have been made during normal operation between on onehand an electrode according to the invention having three edges, i.e. apointed electrode according to FIG. 3, and on theother hand aconventional cylindric and conically pointed electrode. The tests werecarried out on a workpiece requiring a great number of very short welds,i.e. a great number of initiations. For each type of electrode thenumber of correct initiations were counted up to the point whereinitiating problems of the above-mentioned nature appeared. Thecylindric and conically pointed electrode gave about 80 correctinitiations before any problems appeared, while the electrode accordingto the invention after 800 initiations was still operating withoutfailure. In this connection it was observed that if the point of theelectrode was blunted or broken the excellent initiating characteristicsof the electrode according to the invention were not influenced.

Further, welding tests have been carried out using electrodes accordingto the invention having other cross sections than equilateral trianglesand using known electrodes having spaded or chisel end parts. Althoughthe latter show some longitudinal edges, the edge angles are alwaysobtuse. Besides, these known electrodes have not been given said spadedorjchisel shape giving longitudinal edges to improve the initiatingcharacteristics, but to imply a reduction of the cross section and toincrease the current density of the arc and to make it possible toincrease the welding speed during continuous welding by holding the edgeof the electrode parallel to the longitudinal direction of the weld.

During all these tests the operating conditions were the-following:

The welding chamber was a sealed metal chamber initially evacuated to apressure of 10" torr after which highly purified argon was supplieduntil pressure equalization had occurred. The electrodes consisted ofwolfram with 2 percent thorium oxide, having a diameter of 1.6 mm beforegrinding. The voltage source was a DC .welding set giving an opencircuit voltage of 80V and a current strength of 80 A. The electrode wasconnected to the negative terminal of the voltage source. The distancebetween the electrode and the workpiece was about 1 mm. Theseoperational data are merely exemplifying and are to be considerednon-limiting. Thus, it is possible to use, instead of argon, other inertgases, such as helium.

The tests indicated that a chisel-shaped electrode gave considerablefewer correct initiations than a conventional, conically pointedelectrode. The are showed a clear tendency to move all the way up to theelectrode holder. I

Furthermore, it could be seen that an electrode having four edges and asquarecross section did not give any striking at all. However, anelectrode according to FIG. 6 gave substantially the same efficiency asan electrode having a cross section in the shape of an equilaterialtriangle, the excellent results of which have been mentioned above.

Thus, the electrode according to the invention implies extraordinarilyinitiating characteristics. The initiation or striking will be reliableand will take place in a correct direction. Further, the arc will bestable and will not move upwards on the electrode or wander off ontoadjacent parts of the workpiece. This is most important, when theworkpiece includes a number of upstanding parts between which thewelding electrode has to be lowered.

Furthermore, the electrode according to the invention involves theadvantage that its excellent characteristics will not be deteriorated inany degree worth mentioning if the electrode is broken or its lower endfacing the workpiece is damaged.

Obviously, the invention is not limited to the embodiments described,but changes and modifications can be made without departing from theinvention idea. Thus, the electrodes can have other cross sections thanthose illustrated and the electrodes can consist of other suitablematerials or combinations of materials than wolfram and thorium oxide.Also, the electrodes can have longitudinal edges over their entirelength.

Iclaim:

1. In an inert gas arc welding apparatus including a sealed weldingchamber filled with an inert gas, the workpiece to be welded beingarranged in said chamber and connected to one terminal of a voltagesource, an electrode holder arranged in said chamber and connected tothe other terminal of the voltage source, and a non-consumable electrodemounted in said electrode holder so that the electrode does not touchthe workpiece, the improvement wherein the electrode has the shape of arod with an elongated body, said body having a first end portion havingan extreme end facing the workpiece and a second end portion attached tothe electrode holder so that an arc can be struck between the extremeend of said first end portion and the workpiece, said first end portionhaving at least one edge formed between two contiguous longitudinallyextending surfaces formed by a portion of said rod elongated body andstarting from said extreme end and extending along the length of thefirst end portion, the edge angle formed by the two surfaces divergingfrom the edge being essentially less than each cross-section of saidfirst end portion having the shape of an equilateral triangle, wherebythe initiating characteristics are improved.

2. In an inert gas arc welding apparatus including a sealed weldingchamber filled with an inert gas, the workpiece to be welded beingarranged in said chamber and connected to one terminal of a voltagesource, an electrode holder arranged in said chamber and connected tothe other terminal of the voltage source, and a non-consumable electrodemounted in said electrode holder so that the electrode does not touchthe workpiece, the improvement wherein the electrode has the shape of arod with an elongated body, said body having a first end portion havingan extreme end facing the workpiece and a second end portion attached tothe electrode holder so that an arc can be struck between the extremeend of said first end portion and the workpiece, said first end portionhaving at least one edge formed between two contiguous longitudinallyextending surfaces formed by a portion of said rod elongated body andstarting from said extreme end and extending along the length of thefirst end portion, the edge angle formed by the two surfaces divergingfrom the edge being essentially less than 90, each cross-section of saidfirst end portion having the shape of a regular figure having fourangles connected by concave lines, whereby the initiatingcharacteristics are improved.

3. The apparatus of claim 2 wherein the at least one edge angle formedby two surfaces diverging from the edge is about 60.

4. In an inert gas arc welding apparatus including a sealed weldingchamber filled with an inert gas, the workpiece to be welded beingarranged in said chamber and connected to one terminal of a voltagesource, an electrode holder arranged in said chamber and connected tothe other terminal of the voltage source, and a non-consumable electrodemounted in said electrode holder so that the electrode does not touchthe workpiece, the improvement wherein the electrode has the shape of arod with an elongated-- body, said body having a first end portionhaving an extreme end facing the workpiece and a second end portionattached to the electrode holder so that an arc can be struck betweenthe extreme end of said first end portion and the workpiece, said firstend portion having at least one edge formed between two contiguouslongitudinally extending surfaces formed by.a portion of said rodelongated body and starting from said extreme end and extending alongthe length of the first end portion, each cross-section of said firstend having a triangular shape with angles of about whereby theinitiating characteristics are improved.

1. In an inert gas arc welding apparatus including a sealed weldingchamber filled with an inert gas, the workpiecE to be welded beingarranged in said chamber and connected to one terminal of a voltagesource, an electrode holder arranged in said chamber and connected tothe other terminal of the voltage source, and a non-consumable electrodemounted in said electrode holder so that the electrode does not touchthe workpiece, the improvement wherein the electrode has the shape of arod with an elongated body, said body having a first end portion havingan extreme end facing the workpiece and a second end portion attached tothe electrode holder so that an arc can be struck between the extremeend of said first end portion and the workpiece, said first end portionhaving at least one edge formed between two contiguous longitudinallyextending surfaces formed by a portion of said rod elongated body andstarting from said extreme end and extending along the length of thefirst end portion, the edge angle formed by the two surfaces divergingfrom the edge being essentially less than 90*, each cross-section ofsaid first end portion having the shape of an equilateral triangle,whereby the initiating characteristics are improved.
 1. In an inert gasarc welding apparatus including a sealed welding chamber filled with aninert gas, the workpiecE to be welded being arranged in said chamber andconnected to one terminal of a voltage source, an electrode holderarranged in said chamber and connected to the other terminal of thevoltage source, and a non-consumable electrode mounted in said electrodeholder so that the electrode does not touch the workpiece, theimprovement wherein the electrode has the shape of a rod with anelongated body, said body having a first end portion having an extremeend facing the workpiece and a second end portion attached to theelectrode holder so that an arc can be struck between the extreme end ofsaid first end portion and the workpiece, said first end portion havingat least one edge formed between two contiguous longitudinally extendingsurfaces formed by a portion of said rod elongated body and startingfrom said extreme end and extending along the length of the first endportion, the edge angle formed by the two surfaces diverging from theedge being essentially less than 90*, each cross-section of said firstend portion having the shape of an equilateral triangle, whereby theinitiating characteristics are improved.
 2. In an inert gas arc weldingapparatus including a sealed welding chamber filled with an inert gas,the workpiece to be welded being arranged in said chamber and connectedto one terminal of a voltage source, an electrode holder arranged insaid chamber and connected to the other terminal of the voltage source,and a non-consumable electrode mounted in said electrode holder so thatthe electrode does not touch the workpiece, the improvement wherein theelectrode has the shape of a rod with an elongated body, said bodyhaving a first end portion having an extreme end facing the workpieceand a second end portion attached to the electrode holder so that an arccan be struck between the extreme end of said first end portion and theworkpiece, said first end portion having at least one edge formedbetween two contiguous longitudinally extending surfaces formed by aportion of said rod elongated body and starting from said extreme endand extending along the length of the first end portion, the edge angleformed by the two surfaces diverging from the edge being essentiallyless than 90*, each cross-section of said first end portion having theshape of a regular figure having four angles connected by concave lines,whereby the initiating characteristics are improved.
 3. The apparatus ofclaim 2 wherein the at least one edge angle formed by two surfacesdiverging from the edge is about 60*.